Booklets or brochures in the form of a stack of paper sheets joined together and folded along a middle line are usually manufactured by collecting the sheets and stitching them together, using, e.g. wire stitching. Either the sheets are folded separately before collecting or the stack is folded after stitching. There are also apparatus in use for stitching continuously moving paper stacks. The disadvantage of stitched booklets is the fact that their fold region has an increased thickness. This is not so much the case for booklets from paper sheets which are adhesively joined together. Furthermore, wire stitched booklets contain foreign material which is unwanted for recycling. This also is not the case for booklets with adhesively joined pages.
There are known processes for adhesively joining paper layers but either they cannot be adapted for production speeds such as are necessary for continuously processing the output of a modern rotary printing press or else they require very complicated apparatus.